Um Ik-Hwan, Lee Ji-Youn, Kim Han-Tae, Bae Sun-Kun
Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea.
J Org Chem. 2004 Apr 2;69(7):2436-41. doi: 10.1021/jo035854r.
Second-order rate constants have been measured for alkaline hydrolysis of O-aryl thionobenzoates (X-C(6)H(4)-CS-OC(6)H(4)-Y) in 80 mol % H(2)O-20 mol % DMSO at 25.0 +/- 0.1 degrees C. The Hammett plot for the reaction of O-4-nitrophenyl X-substituted thionobenzoates (X-C(6)H(4)-CS-OC(6)H(4)-NO(2), 1a-e) exhibits a downward curvature. However, a possible traditional explanation in terms of a change in the rate-determining step (RDS) has been considered but rejected. The proposed explanation involves stabilization of the ground-state (GS) through-resonance interaction between the electron-donating substituent X and the thionocarbonyl functionality on the basis of the linear Yukawa-Tsuno plot obtained for the same reaction. The Brønsted-type plot for the reaction of O-aryl thionobenzoates (C(6)H(5)-CS-OC(6)H(4)-Y, 2a-i) is linear but exhibits many scattered points with a small beta(lg) (-0.35). The Hammett plot for the same reaction shows rather poor correlation with sigma(-) constants but much better correlation with sigma(o) constants. The alkaline hydrolysis of O-aryl thionobenzoates (1a-e and 2a-i) has been proposed to proceed through an addition intermediate in which bond formation is the RDS.
已在25.0±0.1℃下，于80摩尔%的H₂O - 20摩尔%的二甲基亚砜中测定了O - 芳基硫代苯甲酸酯（X - C₆H₄ - CS - OC₆H₄ - Y）碱性水解的二级速率常数。对于O - 4 - 硝基苯基X - 取代硫代苯甲酸酯（X - C₆H₄ - CS - OC₆H₄ - NO₂，1a - e）反应的哈米特图呈现向下的曲率。然而，关于速率决定步骤（RDS）变化的一种可能的传统解释已被考虑但被否决。所提出的解释基于同一反应得到的线性汤川 - 津野图，涉及供电子取代基X与硫代羰基官能团之间通过共振相互作用对基态（GS）的稳定作用。O - 芳基硫代苯甲酸酯（C₆H₅ - CS - OC₆H₄ - Y，2a - i）反应的布朗斯特型图是线性的，但有许多分散的点，β(lg)较小（-0.35）。同一反应的哈米特图与σ⁻常数的相关性相当差，但与σ⁰常数的相关性要好得多。已提出O - 芳基硫代苯甲酸酯（1a - e和2a - i）的碱性水解通过加成中间体进行，其中键的形成是速率决定步骤。
